whats urea??? how does the clean diesel emissions system work?
The ammonia in the urea combines with the NOx to form something else. Works more effectively in bigger vehicles with bigger displacement engines (Touareg, Audi Q7, and such). I'm no chemist, and I can't remember what it transforms into, but ammonia is involved. It's just black magic, evil juju to me.
The smaller diesels (Jetta and Golf sized) won't have the urea injection systems. Their NOx production rate differs enough that they'll use an "afterburner" to periodically burn up the particulates and NOx captured in a trap. That one apparently still has teething problems that have delayed the early 2007 introduction of the 2008 TDI models until....2008.
Solving the diesel emissions 'problem' was forced by insisting that the diesel vehicles adhere to the same emissions requirements as gasoline engined vehicles, and about time. That means soot, particulate, and Nox emissions, formerly relatively lenient for diesels, are much tighter. VW's claim is that their emissions control system for the 2008 models, whenever they finally come out,will have their diesel at lower emissions than the 'traditional' hybrids of Prius and Insight.
I now have my 4th and 5th TDI, My first was totaled, second was sold at 300k miles (still running at 350k+ last time I spoke with the new owner), third was totaled, fourth is my present wagon ($3300), and I recently picked up a 98 Jetta TDI ($2500).
Problem cars? Not to me. Maybe I've just gotten better with all the practice.